The overall goal is to elucidate further the causes of abnormal prenatal development through the study of spontaneous abortions of known karyotype and morphology. Risk factors will be derived from analyses of the extensive and systematic histories collected for about 2700 women with chromosomally normal (euploid) and chromosomally abnormal (aneuploid) spontaneous abortions and 4400 control women delivering at 28 weeks gestation or later. These data were collected over a twelve year period in three New York City hospitals. Analyses of these data, throughout the period of collection, have yielded a number of insights on determinants for euploid and aneuploid spontaneous abortion. Further analyses are proposed to replicate and elaborate some associations, to explore inconsistencies further (over time or with sociodemographic characteristics) in the associations of other exposures with spontaneous abortion, and to examine new research questions. The specific aims are to: describe the epidemiology of euploid spontaneous abortion, including a first effort to study systematically risk factors for fetal and non-fetal losses; describe the epidemiology of trisomy; examine whether nausea is an indicator of the viability of the pregnancy; for length of time to conception, to identify risk factors, and seek associations with karyotype; analyze data relating to DNA adduct formation in the fetuses of smokers; develop a systematic study of early (subclinical) pregnancy loss.